Multiple-channel image dissector tube



July 25, 1967 R. s. NIELSEN MULTIPLE-CHANNEL IMAGE DIssEcToR TUBE Filed April l0, 1964 BJEcr e//Azo BY Us MM f J .Jn m, F

United States Patent O 3,333,145 MULTIPLE-CHANNEL IMAGE DISSECTOR TUBE Reinald S. Nielsen, Carlisle, Mass., assignor to the United Y States of America as represented by the Secretary of the Air Force Filed Apr. 10, 1964, Ser. No. 358,967 Claims. (Cl. 315-10) ABSTRACT OF THE DISCLOSURE This invention relates generally to optical image analysis apparatus wherein an electron analog of an optical image is systematically sampled, and, more particularly, to an image dissector tube having a plurality of independent, simultaneous, output signal channels.

An image dissector tube is used to scan optical images to create input signals for a variety of signal processing systems. In current art, an image dissector tube is employed, typically, as an element of a television channel; an electron analog of the scene to be televised is caused to pass across a single aperture in a metal plate. Electrons passing through the aperture constitute a measure of the electron image density. With the electron image regularly passed across the aperture in the marmer standardized by present television art, the electrons passing through the aperture become the single output video signal. Since there is only one aperture, prior art image dissector tubes require but one amplifier for the electron stream passing through the aperture. Any of a variety of electron multiplier devices have been employed to amplify the electron stream.

A multiple signal channel optical image analysis apparatus has extensive utility, inter alia, in an input-output station for a large digital computer, in large capacity read-only digital computer memories, optical character recognition apparatus, and in microdensitometers.

However, an image dissector tube with more than one aperture to provide a plurality of independent output signals is not known in the prior art. Conventional electron multiplier devices are excessively bulky for use in a multichannel image analysis apparatus. Typically, the holes in an aperture plate are a few thousandths of an inch in vdiameter spaced from one another with similar dimensions. The first dynode of the electron multiplier must Vbe large enough to intercept all electrons passing through the aperture; this implies an entrance dimension greater than the aperture if the dynode is not flush with the aperture plate. For apertures of practical value (0.0005 0.005" approximately), interference between electron multipliers is encountered when conventional electron `multipliers are employed. The individual electron multipliers must4 be small, carefully aligned with the aperture holes, `relatively similar in multiplication factor, and robust enough to withstand normal handling of the optical Vimage analysis apparatus.

Accordingly, it is a primary object of the present inlventionto provide an image dissector tube having an improved electron amplifier device which has a plurality -of `independent output signal channels and is of rugged mechanical structure while simple and inexpensive to manufacture.

Another object of this invention is to provide an image dissector tube having an electron amplifier of a design whereby very close dimensional tolerances can be maintained between a plurality of apertures.

Still another object of this invention is to provide an improved image dissector tube wherein alignment variance of a plurality of apertures in said tube is minimized.

And still another object of this invention is to provide a multiple channel image dissector tube having an improved electron multiplier with fewer electrical connections than the number required with conventional electron multiplier devices.

To the accomplishment of the foregoing objects and other advantages, the present invention, in brief, comprehends the utilization of a solid, electrical insulator material in which a plurality of individual holes are pierced to serve as sampling apertures for an electron image. With appropriate orientations for the plurality of holes, a conventional electron multiplier is associated with each aperture. In this manner, an image dissector tube having a multiplicity of simultaneous independent output video signals is constructed.

The invention and the above-noted objects and other features thereof will be understood more clearly and fully from the following detailed description with reference to the accompanying drawings, in which:

FIG. 1 is a schematic representation of the preferred embodiment;

FIG. 1A is an elevation View of a 4-hole aperture plate;

FIGS. 2A and 2B are elevation and plan views of an 8-hole aperture plate; and

FIG. 3 is a schematic of the circuitry in a multiple channel image dissector tube.

Now referring to FIG. 1, image dissector tube 10 employs a vacuum enclosure (glass cylinder, typically) 16, containing photo-cathode 15, accelerator anode 13, aperture plate 20 having apertures 31, 32, and 33, and associated electron amplifiers 41, 42, and 43. Magnetic focus and deflection coils 14 are typically employed outside glass cylinder 16. In operation, an optical image is focused on photo-cathode 15. Photo-cathode 15 emits electrons in proportion to the illuminating ux density; hence, an electron replica of the optical image exists in the vicinity of the photo-cathode. Accelerator anode 13 is held at a potential positive relative to photo-cathode 15. The positive potential field causes the electrons emitted by the photo-cathode to be accelerated toward anode 13 and, hence, toward aperture plate 20. An electric current in focus coil 14 is adjusted, relative to the electron accelerating potential field, to achieve a condition of focus for electrons arriving at aperture plate 20. Typically, the electron image at photo-cathode 15 is imaged with unity magnification at aperture plate 20.

The electronic image is scanned magnetically in the plane of apertures 31, 32 and 33, and thus photo-electrons released by different picture elements of the scene enter the aperture of the electron multiplier. Holes 31, 32, and 33 in aperture plate 20 permit passage of electrons from the electron image to electron amplifiers 41, 42, and 43. An output signal proportional to electron image density is available at the output of each amplifier.

The simultaneous output signals from electron amplifiers 41, 42, 43 correspond to image values at known adjacent points in the image.

A three-aperture configuration similar to FIG. l has great utility in curve following. For example, from an array of three apertures lying on an axis effectively normal to the scan direction, the apertures move from left to right along the line of the scan direction. When a hole pair encounters the boundary of the image (here, the curve being traced), one hole is initially affected with the second hole recognizing the boundary shortly thereafter. With a known scanspeed and known distance between holes (on an axis normal to the scan direction), a measure of the image boundary slope is easily derived; i.e., the displacement normal to the scan axis relative to displacement along the scan axis. In effect, the measure of theV slope amounts to measuring the time interval between the instant the first hole encounters the image boundary and the instant the second hole encounters the boundary. From the array of three holes, two slope values are measured. The difference of these slope values yields a measure of image boundary curvature. In deriving slope and curvature measurements, it is convenient to count timing pulses during the intervals between successive aperture boundary transition. These timing pulse count values are accepted directly by a digital computer.

Typically, the aperture dimensions range from one-half to several thousandths of an inch. This is because the reproduction of fine detail in the optical image is determined by the relation of aperture size to photo-cathode size. In general, a line can be resolved whose width is approximately equal to the diameter of a round aperture. Hence, for resolution of a maximum number of lines in an image accommodated by the photo-cathode (one to five inches, typically), the smallest practical aperture dimension is sought.

Apertures may be circular, rectangular, etc. The individual apertures are typically spaced from one another by a distance equal to the major aperture dimension. That is, two 0.005-inch diameter apertures are spaced 0.010 inch on centers.

FIGS. 2A and 2B represent an aperture configuration optimized for reading digital data recorded on photographic film. The unique construction of aperture plate 50 permits practical use of eight independent electron multiplier amplifiers. In FIG. 2A, 59 is the insulating material which can be, inter alia, quartz, glass or ceramic. Typically circular aperture plates are used to conform to the shape of glass enclosure 16, but this configuration is not crucial.

Eight holes 53 pierce aperture plate forward surface 59 facing photo-cathode 15; the eight holes are in line 12 (FIG. 2A). On the reverse surface of plate 50, the holes are dispersed in an appropriate manner 53a as discussed below. The interior of holes 53 are treated to create a conductive surface with an electron secondary emission ratio of unity or greater. Electrical connection to the conductive interior surface of each hole 53 is achieved by means of conductive pad 55 and a (typically) common conductive terminal S4 (FIG. 3) on forward surface 59.

FIG. 3 is a schematic representation of optical image analysis apparatus employing the present invention. For simplicity only two apertures are shown in FIG. 3. (Reference numbers in the ligure refer to similar elements in the earlier figures.) Multiple apertures 53 along line 12 face photo-cathode 15 disposed beyond accelerating anode 13. Behind aperture plate 50 a single signal anode 47 and an electron multiplier structure 48, with integral signal anode, may be employed; either or both constructions can be employed in a tube. Typically, a single source of high voltage, B, is used to establish operating potentials by means of a resistor divider typified yby R1, R2, and R3. Anode 13 is shown electrically connected to common conductive terminal surface 54 of plate 50; this connection is convenient to use in most circumstances. Anode 13 and surface 54 are operated between a few tens of volts and several hundreds of volts positive with respect to photo-cathode 15. Pad 55 is 100 to several thousand volts positive relative to conductive surface 54. Anode 47 and the first dynode of electron multiplier 48 are from 50 to 200-300 volts positive relative to pad 55. The voltage across the resistor divider associated with multiplier 48 is determined by the type of multiplier employed.

When the internal surface of each of holes 53 has a secondary electron emission ratio sufficiently greater than unity, the hole essentially becomes a channel electron multiplier. (See Continuous Channel Electron Multipliers, G. W. Goodrich, W. C. Wiley; Rev. Sci. Inst. vol. 33, No. 7, pp. 761-762, July 1962.) In this circumstance, the separation of holes 53 (dimension S) in FIG. 2A need be only great enough to accommodate a signal anode 47 of smallest practical dimensions. Mounting difficulties favor an anode large enough to accommodate the expected errors in centering the anode over the holes exits. However, anodes 47 cannot exceed a size that will imply capture of improper electrons. In FIG. 2A, the anode associated with hole 53x must not capture electrons from hole 53y when the maximal assembly errors occur.

Thickness T of plate 50 in FIG. 2B is defined by the requirements of the channel multiplier when holes 53 are operated in that manner. The angle between the axis of holes 53 and the electron line of flight must be held to particular values to achieve proper multiplier action. Hence, with S fixed by consideration of anodes 47, T will be defined by the appropriate trigonometric relation to the required angle between electron Hight and hole axis.

When the interior of holes 53 do not provide for channel multiplier operation, the separation (dimension S) in FIG. 2A is dependent upon the detailed construction of electron multiplier 48. Dimension S is the minimum distance necessary to accommodate the multiplier structures and preclude cross coupling between one hole and another. In FIG. 2A, the multiplier associated with hole 53x must not capture electrons from hole 53y when the maximal assembly errors occur.

A variety of techniques exist for piercing the necessary holes S3 in a body of insulating material and then coating the interior surface with low electrical conductance material. Connecting terminals 54 and 55 for the ends of the holes may be formed by evaporation of any one of several different materials.

Several different elements (lithium, nickel, e.g.) may be used to form the interior low conductive surface of holes 53. Compound materials (silver-cesiumoxide-cesium, silver-antimony-cesium, e.g.) may also be used. Also, glass (silicon compounds) with electrical conductivity greater than the solid body may be used to create a satisfactory interior surface for holes 53. The choice of the appropriate material is determined by the desired operating condition of the instant invention.

Optical image analysis employs measurements of the variation in image density. Therefore, when a multiple aperture image analysis apparatus is employed, the gain of each aperture must be known. Particularly, it is convenient to have the gain of each aperture signal channel equal to one known value. In the following discussion, aperture signal channel gain is taken to be the image analyzer signal output (amperes) for a given illuminant flux input (watts). Electron multipliers characteristically approximate a current source.

The electron image analyzer device can be operated in a channel multiplier mode with means for independent adjustment of the potential applied across each aperture. That is to say, the potential from each conductive 55 pad to common terminal 54 of FIG. 3 is independently adjustable for each aperture. Variability in the multiplication characteristics of the material in the holes leads to unavoidable differences in gain between separate apertures; this effect is compounded by the variations in hole length due to the compromise between hole separation S `and the desired aperture pattern, for example, the line array 12.

Conventional electron multiplier structures require an individual electrical connection to each dynode. The channel multiplier requires two connections only. Hence, an advantageous reduction in the number of electrical connections is achieved when holes 53 are operated las channel multipliers.

Holes 53 of approximately circular cross-section are often easier to create than arbitrary cross-sections such as rectangles, etc. Were holes 53 in FIG. 2B ideally circular, their intersection 52 with an ideal surface 54 would be elliptical. When a proper ellipse cannot be achieved or is not satisfactory, an auxiliary metal plate can be secured to surface 54. Holes of the appropriate cross-section (rectangular, circular, etc.) may be pierced in the auxiliary plate on centers that will align them with the holes along line 12 (FIG. 2A). FIG. 1A is another embodiment consisting of 4 apertures 70 arranged at the corners of a square lying in the face of solid body closest to the photo-cathode.

While there has been shown and described and pointed out the fundamental novel features of the invention as applied to the preferred embodiment, it will be understood that various omissions and substitutions and changes in the form and details of the device and construction methods may be made by those skilled in the arts without departing from the spirit of the invention.

For example, the eight-hole aperture configuration shown in FIG. 2A has utility as a read-only digital computer memory by substituting a modified digital data slide for the object shown in FIG. 1. Essentially, the apertures are centered on photographic tracks that have digital data in the pattern of transparent and opaque segments. The output from two holes are used to control the lateral position of all the apertures as the data is scanned. In this form, it is practical to create a memory capacity of 108 to 109 data bits with a random access time to any bit in a 20-millisecond interval.

This particular arrangement not only obviates the impossibly tight dimensional tolerances encountered if simple mechanical registration of the recorded data with a reading device were attempted, but also use of the multiple channel image dissector tube affords data reading rates ve to ten times greater than those available with present equipment.

Those skilled in the art will recognize the utility of many more holes than the eight discussed here. Some applications of the device will benefit from as many as 128 or 256 independent apertures.

It is the intention, therefore, to be limited only by the scope of the following claims.

I claim:

1. An image analysis tube comprising: a photo-cathode means for scanning an electron image formed at said cathode, means responsive to the electron density at known adjacent positions of said electron image, and independent signal channel means for each of said adjacent electron density responsive means.

2. The apparatus described in claim 1 wherein said means responsive to the electron density at known adjacent points of said electron image comprises a solid insulating body having a plurality of apertures disposed therein in a predetermined manner, and wherein said independent signal channel means comprises a low electrically conductive coating in the walls of said apertures, an electrically conductive coating on one face of said solid body, said conductive coating in electrical connection with said conductive coating in the walls of said apertures, individual electrical terminal means for each of said aper tures on the opposite surface of said solid body, each of said terminal means in electrical connection with said conductive coating in the walls of said apertures, and output means to provide la plurality of independent output signals to be fed to a utilization device.

3. The apparatus described in claim 2 wherein said plurality of apertures includes apertures in a line lying in the face of said solid body closest to said photo-cathode.

4. The apparatus described in claim 2 wherein said plurality of apertures consists o f three apertures arranged at the apices of an equilateral triangle lying in the face of said solid body closest to said photocathode.

5. The apparatus described in claim 2 wherein said plurality of apertures consists of four apertures arranged at the corners of a square lying in the face of said solid body closest to said photo-cathode.

6. The apparatus described in claim 2 wherein the bounding walls of said apertures is of greater length than the width of said apertures, and the center-to-center spacing of said apertures is on the order of twice the diameter of said apertures.

7. The apparatus described in claim 2 wherein said conductiVe coating on the interior wall of each of said aperd tures has an electron secondary emission ratio of unity or greater.

8. The apparatus described in claim 2 wherein said output signal means comprises a conductive anode associated with each of said plurality of apertures.

9. The apparatus described in claim 2 wherein said output signal means comprises electron multiplier means associated with each of said plurality of apertures.

10. The apparatus described in claim 2 which further includes a separate plate dening the eifective cross-section of the entry to the said apertures in said solid body.

References Cited UNITED STATES PATENTS 4/1964 Goodrich 316-68 X 9/ 1966 Moore 340--324 

1. AN IMAGE ANALYSIS TUBE COMPRISING: A PHOTO-CATHODE MEANS FOR SCANNING AN ELECTRON IMAGE FORMED AT SAID CATHODE, MEANS RESPONSIVE TO THE ELECTRON DENSITY AT KNOWN ADJACENT POSITIONS OF SAID ELECTRON IMAGE, AND INDEPENDENT SIGNAL CHANNEL MEANS FOR EACH OF SAID ADJACENT ELECTRON DENSITY RESPONSIVE MEANS. 